It was adopted by the Austrian Army as the StG 77 (Sturmgewehr 77) in 1978,[3] where it replaced the 7.62×51mmStG 58automatic rifle (a licence-built FN FAL).[4] In production since 1978, it is the standard small arm of the Austrian Bundesheer and various national police units. Its variants have also been adopted by the armed forces of dozens of countries.

The AUG has a rotating bolt that features 7 radial locking lugs and is unlocked by means of a pin on the bolt body and a recessed camming guide machined into the bolt carrier. The bolt carrier itself is guided by two guide rods brazed to it and these rods run inside steel bearings in the receiver. The guide rods are hollow and contain the return springs. The bolt also contains a claw extractor that forms the eighth locking lug and a spring-loaded "bump"-type casing ejector.

The gas cylinder is offset to the right side of the barrel and works with one of the two guide rods. The AUG uses a short-stroke piston system where the right guide rod serves as the action rod, transmitting the rearward motion of the gas-driven piston to the bolt carrier. The left-hand rod provides retracting handle pressure when connected by the forward assist and can also be utilized as a reamer to remove fouling in the gas cylinder. The firearm uses a 3-position gas valve. The first setting, marked with a small dot, is used for normal operation. The second setting, illustrated with a large dot, indicates fouled conditions. The third, "GR" closed position is used to launch rifle grenades (of the non-bullet trap type).

The AUG is hammer-fired and the firing mechanism is contained in the rear of the stock, near the butt, covered by a synthetic rubber shoulder plate. The hammer group is made entirely of plastics except for the springs and pins and is contained in an open-topped plastic box which lies between the magazine and the buttplate. During firing the recoiling bolt group travels over the top of it, resetting the hammer. Since the trigger is located some distance away, it transmits its energy through a sear lever which passes by the side of the magazine. The firing pin is operated by a plastic hammer under pressure from a coil spring.

Steyr AUG with a German KCB-77 M1 bayonet.

Steyr AUG with a loaded 30-round magazine.

The Steyr AUG's telescopic sight picture. Note the backup iron sights on top of it.

The AUG features an Spz-kr type progressive trigger (pulling the trigger halfway produces semi-automatic fire, pulling the trigger all the way to the rear produces fully automatic fire) and a safety mechanism (cross-bolt, button type), located immediately above the hand grip.[5] In its "safe" position (white dot) the trigger is mechanically disabled; pressing the safety button to the left exposes a red dot and indicates the weapon is ready to fire. Some versions have an ALO or "automatic lockout", a small projection at the base of the trigger. This was first included on the Irish Defence Forces variant of the rifle, and soon after, the Australian Defence Forces variant. In the exposed position the ALO stops the trigger being squeezed past the semi-automatic position. If needed, the ALO can be pushed up to permit automatic fire.[6]

The AUG is fed from a translucent, double-column box magazines (molded from a high-strength polymer) with a 30-round capacity and an empty weight of 130 g (4.6 oz). The light machine gun version of the AUG uses an extended 42-round magazine. An Argentine variant of the FN FAL chambered in 5.56×45mm NATO cartridge and known as the FALMP III Type 2 also uses the same magazine.

The AUG has a 1.5× telescopic sight that is integrated with the receiver casting and is made by Swarovski Optik.[5] It contains a simple black ring reticle with a basic rangefinder that is designed so that at 300 m (984.3 ft) a 180 cm (5.11 ft) tall man-size target will completely fill it, giving the shooter an accurate method of estimating range. The sight cannot be set to a specific range but can be adjusted for windage and elevation for an initial zero and is designed to be calibrated for 300 m. So when it is set, aiming at the center of a target will produce a hit at all ranges out to 300 m. It also has a back-up iron sight with a rear notch and front blade, cast into the top of the aluminium optical sight housing, used in case of failure or damage to the primary optical sight. The sight is also equipped with a set of three illuminated dots (one on the front blade and two at the rear) for use in low-level lighting conditions. In order to mount a wide range of optics and accessories, a receiver with a NATO-standard Picatinny rail and detachable carrying handle was also developed and introduced in December 1997.

The quick-change barrel used in the AUG is cold hammer-forged by GFM-GmbH of Steyr Austria for increased precision and durability, its bore, chamber and certain components of the gas system are chrome-plated. The standard rifle-length barrel features 6 right-hand grooves and a rifling twist rate of 228 mm (1:9 in). An external sleeve is shrunk on to the barrel and carries the gas port and cylinder, gas valve and forward grip hinge jaw. There is a short cylinder which contains a piston and its associated return spring. The barrel locks into a steel insert inside the receiver through a system of eight lugs arranged around the chamber end and is equipped with a folding, vertical grip that helps to pivot and withdraw the barrel during barrel changes. The most compact of the barrels has a fixed vertical grip.

The receiver housing is a steel-reinforced aluminium extrusion finished with a baked enamel coating.[5] It holds the steel bearings for the barrel lugs and the guide rods. The non-reciprocating plastic cocking handle works in a slot on the left side of the receiver and is connected to the bolt carrier's left guide rod. The cocking handle has a forward assist feature—alternatively called a "silent cocking device"—used for pushing the bolt shut without recocking the rifle.[5][7] A bolt hold-open device locks the bolt carrier assembly back after the last round has been fired.[7] The newer AUG A3s possess a bolt release button, prior to this development all AUGs and the USR required the cocking handle being retracted to release the bolt group after a new magazine has been inserted. Older versions of the AUG can be upgraded to use the newer A3 stock and in turn the button release; however, it requires they also upgrade other key parts as well including the hammer pack.

The rifle's stock is made from fiberglass-reinforced polyamide 66. At the forward end is the pistol grip with an enlarged forward trigger guard completely enclosing the firing hand that allows the rifle to be operated with winter gloves.[5] The trigger is hung permanently on the pistol grip, together with its two operating rods which run in guides past the magazine housing. Behind that is the locking catch for the stock group. Pressing this to the right will separate the receiver and stock. The magazine catch is behind the housing, on the underside of the stock. Above the housing are the two ejector openings, one of which is always covered by a removable strip of plastic. The rear of the stock forms the actual shoulder rest which contains the hammer unit and the end of the bolt path. The butt is closed by an endplate which is held in place by the rear sling swivel. This swivel is attached to a pin which pushes in across the butt and secures the plate. There is a cavity under the buttplate that holds a cleaning kit.

While the AUG is not fully ambidextrous, it can still be configured to be use for left- or right-handed operators by changing the bolt with one that has the extractor and ejector on the appropriate side, and moving the blanking plate to cover the ejection port not in use. However, there exists also a right-hand-only stock that allows for the use of M16 type STANAG magazines.[8][9]

The AUG's receiver may also be changed from the standard model with a carrying handle and built-in 1.5× optical sight,[10] to the "T" model receiver which has a universal scope mount to allow for the use of a variety of scopes and sights.[10] The rifle also has several different types of receivers with Picatinny rails.[11] It has proven to be an effective sniper or designated marksman rifle when configured with the 621 mm (24.4 in) light machine gun barrel, the universal scope mount fitted with a Kahles ZF69 6×42 optical sight and the semi-auto-only trigger group.

The AUG's firing mechanism may also be changed at will, into a variety of configurations, including semi-auto and full-auto, semi-auto and three-round-burst, semi-auto-only, or any other combination that the user may desire.[10] It may also be converted into an open-bolt full-auto-only mode of fire, which allows for improved cooling and eliminates cook off problems when the AUG is used as a light machine gun or squad automatic weapon.[10]

In 2014 the Irish Army began issuing upgraded Steyr AUG bullpup assault rifles to its operational units. The modularity of the AUG allowed the Irish AUG A1 model rifles to be modernized without any gunsmithing, by replacing the original A1 housing/receiver group (with 1.5× optical sight) with an A3 housing/receiver group (with MIL-STD-1913 Picatinny rail on top and right side) allowing a modern optical sight to be fitted. The Trijicon ACOG 4× sight was selected as the new optical sight. The upgraded rifles are called the Steyr AUG Mod 14.

The Australian's F88 version of the AUG was tested with a new grenade launcher specifically designed for it called the ML40AUS GLA (Grenade Launcher Assembly), one of the lightest underbarrel grenade launchers at less than 1 kg (2.2 lb) due to steel, aluminium, and synthetic parts. The GLA is mounted on the rifle's bottom accessory rail with the trigger moving through a removable plug in the trigger guard that allows for operation of the launcher inside of it, moving it further back than other launchers to maintain center of balance and improve handling. The ML40AUS differs from the M203 by having a side-opening breech to allow for longer grenade rounds, a cross-bolt safety, and a new quadrant sight that mounts to the top rail alongside the rifle's optics.[12] On 21 January 2014 however, Thales announced they had instead selected the Steyr SL40 grenade launcher due to "significant" engineering concerns with the ML40AUS. The SL40 is a derivative of the Steyr GL40 launcher designed specifically for the EF88. It weighs 1.025 kg (2.26 lb) and has a 180 mm (7.1 in) long barrel. Though marginally heavier than the ML40AUS, it has the same attachment, firing mechanism, and control layout.[13]

The New Zealand Army adopted the F88 Austeyr and made some modifications. It differs from the Australian version in several ways. One of the more notable is that it has three fire settings (off, single, auto), whereas the Australian version has two (off, and a single-auto setting depending on how far the trigger is pressed).[14]

AUG: The Steyr AUG is the standard assault rifle model and is chambered in 5.56×45mm NATO cartridge. It was introduced in 1978 and was adopted by the Austrian Army and designated it as the StG 77 in 1978, then it was later adopted by several military agencies around the world.

AUG A1: The Steyr AUG A1 is an improved variant of the AUG and was introduced in 1982. It is available with a choice of olive or black furniture.[15]

AUG A2: The Steyr AUG A2 is similar to the AUG A1 but features a redesigned charging handle and a detachable telescopic sight which can be replaced with a MIL-STD-1913 rail.[15] It was introduced in December 1997.

AUG A3: The Steyr AUG A3 is similar to the AUG A2 but features a MIL-STD-1913 rail on top of the receiver and an external bolt release.[16]

AUG A3 SF: The Steyr AUG A3 SF, also known as the AUG A2 Commando or StG 77 A2, is similar to the AUG A2 but features MIL-STD-1913 rails mounted on the telescopic sight and on the right side of the receiver, and includes an external bolt release.[17] The integrated telescopic sight is offered in 1.5× or 3× magnification. It was adopted by the Austrian Special Forces (Jagdkommando) in late 2007.[18]

Based on the AUG, Steyr developed the 9mm AUG submachine gun variant. It is an automatic, blowback-operated model that fires from a closed bolt, and is chambered in 9×19mm Parabellum cartridge. Unlike the rifle variants, it has a unique 420 mm (16.5 in) barrel with six right-hand grooves at a 250 mm (1:9.8 in) rifling twist rate, ended with a recoil compensator, a slightly different charging handle and a magazine well conversion insert enabling the use of standard 25-round box magazines from the Steyr MPi 81 and TMP submachine guns. A conversion kit used to transform any rifle variant into the submachine gun is also available. It consists of a barrel, bolt, adapter insert and magazine.

AUG Para: The Steyr AUG Para, also known as the AUG SMG or AUG 9mm is chambered in 9×19mm Parabellum cartridge and produced since 1988.[1] It differs from the A1 model by the: barrel, bolt, magazine and a magazine well adapter, which allows the rifle to feed from Steyr MPi 69 magazines. This variant operates as a blowback firearm, without the use of the rifle's gas system.[19] For some time a kit of the above components was available to convert any AUG into a 9mm variant.[20]

AUG A3 Para XS: The Steyr AUG A3 Para XS is 9mm variant of the AUG A3 and is similar to the AUG Para. It features a 325 mm (12.8 in) barrel and a Picatinny rail system.[21]

The light machine gun variant can be modified to fire from an open bolt (called the AUG LMG in this configuration). To accomplish this, a modified bolt carrier, striker and trigger mechanism with sear are used.

AUG LSW: The Steyr AUG LSW (Light Support Weapon) is a family of light support versions of the AUG A1.

AUG LMG The Steyr AUG LMG (Light Machine Gun) is based on the AUG HBAR and fires from an open bolt to allow sustained fire, its telescoping sight has a 4× magnification rather than the 1.5× magnification of the base AUG.

AUG LMG–T: The Steyr AUG LMG–T (Light Machine Gun-Telescope)is similar to the AUG LMG but with the Special Receiver for a telescopic sight.

AUG HBAR–T: The Steyr AUG HBAR–T is a (Heavy Barreled Automatic Rifle-Telescope) based on the HBAR but with the Special Receiver and fitted with a Kahles ZF69 6×42 optical sight.

Steyr AUG DMR The Steyr AUG DMR is a designated marksman rifle similar to the HBAR but with the bipod attached to the front of the barrel grip instead of the muzzle end of the barrel.[22]

A semi-automatic version of the rifle known as the AUG P is available to the civilian and law enforcement markets. It features a shorter, 407 mm (16.0 in) barrel and a modified bolt, carrier and trigger assembly that will only allow semi-automatic fire. The rifle also has a slightly different optical sight that features a reticule with a fine dot in the centre of the aiming circle, allowing for more precise aiming.

AUG P: A Police semi-automatic only variant of the AUG A1 with a shorter 407 mm (16.0 in) barrel.

AUG P Special Receiver: Similar to the AUG P but features a MIL-STD-1913 rail on top of the receiver.

AUG SA: A semi-automatic only variant of the AUG A1; built for civilian use and import to the US before being banned from importation in 1989.

AUG Z: A semi-automatic only variant, somewhat similar to the AUG A2 and is intended primarily for civilian use.

AUG Z Sport: A semi-automatic only variant, somewhat similar to the AUG Z for shooting use by the BKA in Germany. This version has a special handguard without the typical front grip.

AUG Z A3: First appeared in 2010, a semi-automatic AUG A3 variant.

USR: An AUG A2 modified to meet the former Federal Assault Weapons Ban (AWB) (or Public Safety and Recreational Firearms Use Protection Act) regulations. The primary difference is the omission of the flash hider.

AUG A3 SA USA: A semi-automatic only variant of the AUG A3 with a 407 mm (16.0 in) barrel, made available for the U.S. civilian market in April 2009.[23][24]

AUG A3-CQC: The Steyr AUG A3-CQC was a prototype development of the AUG A3 and was first displayed by Steyr at the SHOT Show 2006. It differs in having a railed handguard attached ahead of the receiver. Due to the need to remove this extra railed section in order to strip the rifle for cleaning it had a quick detach lever mounted on the left side. Due to the concerns over the extra cost and weight, along with potential issues with the reliability and consistency of the detachable handguard, the prototypes received little interest and were last seen promoted by Steyr in 2008 and likely has been cancelled. In total only 5 prototypes were made, four with standard 18-inch barrels, and one with a longer heavy marksman barrel and a 20-round magazine.[25]

AUG A3 M1: A semi-automatic only variant of the AUG A3 SF but with a detachable optical sight which can be replaced with MIL-STD-1913 rails, manufactured in the US by Steyr Arms since October 2014.[26]

An Australian soldier from the 2nd Battalion, The Royal Australian Regiment with the F88SA1 Austeyr fitted with the standard issue and locally made 1.5× power sight.

An Australian soldier briefs a U.S. Navy admiral on the F88 GLA Austeyr. Note: the grenade launcher has been removed and is being held by the Admiral.

The Australian Army adopted the Steyr AUG A1 and made some modifications, and designated it as the F88 Austeyr.

F88: The F88 Austeyr is the standard individual weapon of the Australia Defence Force. It is manufactured under licence from Steyr Mannlicher AG at the Thales Lithgow Small Arms Factory, which is now owned by Thales Australia. It is issued and supplied to the armed forces of Australia and New Zealand and incorporate a cross hair donut sight, it is also in service in 30 different countries.[27] There are changes and differences between the Austrian version and the Australian version. The changes for the Australian version includes a bayonet lug, a 1:7 in rifling pitch as found in the M16A2 assault rifle, optimized for the heavier 62-grain NATO-standard SS109/M855 round and an "automatic lockout" selector that can physically disable the fully automatic position of the two-stage trigger mechanism found on the standard AUG. It has a cyclic rate of fire of around 680–850 rounds per minute (RPM).[28][27] It also won a competition against the prototype of what would become the Bushmaster M17S.

F88C: The F88A1C Austeyr is a carbine variant of the F88 Austeyr that features a shorter 407 mm (16.0 in) barrel. It s generally used as a personal defensive weapon where manoeuvrability is an issue, such as in armoured vehicles.

F88SA1: The F88SA1 Austeyr is a variant of the F88 Austeyr with an integrated Picatinny rail in place of the standard optical sight that allows the attachment of various other sighting devices (night vision scopes, magnified and non-magnified optics such as the ELCAN C79, Trijicon ACOG or Aimpoint).

F88SA1C: The F88SA1C Austeyr is a compact variant of the F88 Austeyr fitted with a Picatinny rail. The rifle has a 407 mm (16.0 in) barrel. Typically issued to front-line combat infantry units with room and weight constraints such as cavalry, Military Police, reconnaissance, light horse, paratroopers and airfield defence guards (RAAF).

F88 GLA: The F88 GLA Austeyr variant is for the Australian Army with an M203 grenade launcher. It features an Inter-bar (armourer attached) interface, an RM Equipment M203PI grenade launcher, and a Knight's Armament quadrant sight assembly to which a Firepoint red dot sight is attached. The bayonet lug and forward vertical grip are not present in this model.

F88T: ADI has developed a training rifle that is chambered in .22 Long Rifle cartridge to be use by the Australian Army. The rifle provides an economical training alternative, with very low ammunition cost, which can be used in environmentally sensitive training areas and ranges where "overshooting" is an issue, and there is a lower risk of injuring instructors and other persons.[29]

DSTOAdvanced Individual Combat Weapon: Experimental weapon combining the barrel, action and magazine of an F88 Austeyr with an enlarged receiver and stock/body that also incorporates a multiple-shot 40 mm grenade launcher.

F88SA2: The F88SA2 Austeyr is an evolutionary upgrade of the current rifle to fulfill an operational capability gap. Deliveries of several thousand were completed in late-2009 to selected units for overseas service. (Afghanistan) Technical improvements in the F88S-A2 include: Modified gas system for increased reliability and increased interoperability with U.S ammo. An enlarged ejection port. A longer Picatinny Rail on top of the weapon, a modified sight housing, a side rail mount for a torch and Night Aiming Device (NAD). The Color of the barrel, sight and barrel assembly has been changed to khaki to reduce the recognition signature.[30]

EF88: The Enhanced F88 (EF88) is part of the LAND 125 Soldier Combat System project and is a significant upgrade to the F88SA2. It was developed and produced at the Australian Defense Industries factory in Lithgow Small Arms Factory, which is now owned by Thales Australia to fulfill current and near future requirements for the Australian Defence Force and is also intended for export (F90). It was first displayed to the public in the middle of 2012 and the initial production was scheduled for 2013, its final design and testing ended later on that year.[31] While internally and externally the EF88 is still similar to the Steyr AUG, it has received many distinctive upgrades and changes. Upgrades include the following:

1. Length of pull has been shortened by 15 mm. (The distance between the stock backplate and the grip; too long and it becomes difficult to handle on close quarters)

2. Longer top rail and a modular lower forend with side and bottom rails.

9. Provision for electronic architecture to allow centralized control and power management of ancillary devices.

10. Primarily uses the side-loading grenade launcher (Steyr-Mannlicher SL40) which can fire all currently available 40 mm low velocity grenades.

11. Improved grenade launcher mount which improves the balance of the weapon.

12. Improved grenade launcher safety, the new KORD RIC (Rifle Input Control) electronic control system made by Thales will also be integrated into the rifle.[30][32][33]

F90: The intended for export version of the EF88. In June 2012, Thales debuted the F90 at the Eurosatory military exhibition in Paris. Key additions include a bottom rail and a detachable side rail, optional compatibility with STANAG magazines, weight savings over the F88SA2 with a base weight of 3.25 kg (7 lb) and the large trigger guard has been reshaped to serve as a vertical foregrip. Thales in partnership with Steyr-Mannlicher are pursuing small arms procurement programs such as the planned replacement of FAMAS rifle used by the French military. F90 variants include Grenadier, Marksman (508 mm (20 in) barrel) and Close Quarters Battle (360 mm (14 in) barrel).[34] Low Rate Initial Production of the F90 began in September 2014.[35] Dasan Manufacturing will be licensed to manufacture them in an effort to bid them to the South Korean military for future replacements of the Daewoo K2.[36]

STG-556: Introduced at the 2007 SHOT Show, the MSAR STG-556 was manufactured by Microtech Small Arms Research Inc. (a subsidiary of Microtech Knives) a AUG A1 clone significantly re-engineered in its working system and principle as it features a bolt hold-open device as seen on the M16 rifle; otherwise the MSAR STG-556 retains the original AUG features, such as feeding from proprietary translucent plastic magazines and having the quick-change barrel option. The STG-556 rifle can be converted from either having a telescopic sight or a MIL-STD-1913 rail. It is available in either civilian (semi-automatic only) configuration, and military and law enforcement (selective fire) configuration.[7][37]

AXR: Revealed at the 2007 SHOT Show, the TPD USA AXR was manufactured by Tactical Products Design Inc. as an AUG A2 clone capable of semi-automatic only fire, aimed for both the civilian and law enforcement markets, and fed by STANAG magazines; the manufacturer sells clear plastic magazines which are STANAG 4179 compliant and will readily fit in any rifle with a compatible magazine catch.[38] The rifle does not have the integral scope, allowing users to use any kind of scopes or laser sights on the Picatinny railing.[39]

Type 68:[40][41] Taiwanese copy of the AUG with notable differences including a smaller trigger guard and the use of iron sights instead of the original's telescopic sight, but it ultimately did not enter service.[42][43]

New Zealand: Used from 1988 until 2017. The first 5,000 weapons delivered were manufactured in Austria by Steyr Daimler Puch. The majority of weapons now in service are the Australian ADI-made Austeyr F88 variant. It is called the IW Steyr (Individual Weapon Steyr) in service of the New Zealand Defence Force.[71] On 12 August 2015 it was announced the Lewis Machine Tools 5.56 mm MARS-L will replace the Steyr AUG after concerns about its performance in Afghanistan.[72]

Tunisia[40][61] The Steyr AUG was chosen since 1978 to be the Primary weapon of the Tunisian Army, The first regular unit to be issued with the AUG A1 was the GTS, later on, the leadership started to arming the National Guard with Sturmgewehr 58 (FN FAL) and the army with the AUG A1/A2/A3 variants, including the Army's Special Forces.

^"Thales debuts new assault rifle – the F90". Press release. Thales. 11 June 2012. Retrieved 11 June 2012. The F90 is identical to the EF88-designated weapon currently being developed by the company for Australia's LAND 125 program, and is based on the F88 platform that has been in service and evolved in Australia since the late 1980s. ... Thales is in cooperation with Austrian company Steyr Mannlicher to pursue specific opportunities, such as the French DGA FAMAS replacement project, utilising Steyr Mannlicher's manufacturing experience and facilities.